Apparatus for the electrical protection of electric discharge tube installations



Aug. 13. 1-940. H 5M1 BARLOW 2.210.889

APPARATUS FOR THE ELECTRICAL PROTECTION OF ELECTRIC DISCHARGE TUBE INSTALLATIONS Filed Sept. 14, 1958 11.11711 N H! I H Inventor fff/ZBAWLa w I Home Patented Aug. 13, 1940 PATENT OFFlCE APPARATUS Fan The. ELECTRICAL rnov TEcrro-N or ELECTRIC DISCHARGE TUBE I INSTALLATIONS Harold Everard Monteagle Barlow,

London,'England Application September 14, 1938, Serial No. 229,975 in Great Britain January 10, 1938 4 Claims.

This invention relates to the electrical protection of gaseous and other electric discharge tubes such, for example, as those used for electric signs, and electric lighting, and of electric 5 valve cathode ray, X-ray and other ray .ap-' pliances, and it has for its object to provide a device which wlllautomatically interrupt the current supply to the discharge tube upon variation or interruption of the current through the '10 discharge tube.

An electrical protective device according to the present invention broadly comprises an electromagnetic relay in the discharge tube circuit,'said relay being operable automatically to interrupt the current supply to the discharge tube as a result of de-energisation upon variation or interruption of the current through. the discharge tube.

In one embodiment of the invention in which 20.8. transformer is employed for supplying the discharge tube thecurrerit input tothe primary winding of thetransformer is interrupted by the action of an electro-ma.gnetic relay in thedischarge tube circuit, 'said normally energised relay 5. operating automatically as'a result of de-energisfation upon variation or interruption of the current through thedischargetube. Thelterrn (dc-,energisationiused in this speci- 'iication is intendedt o' mean both partialand 30. complete de-energisation.

r i practiceone or more, relays or ,a composite rfelay may be used and each such relay may be a 'ldiiferential relay having independently energi'sed electronagnets, the energisation of one lldl electromagnet being: effected by connecting its winding in the dischargetube circuit so that upon reductionfor: interruption of the current through the discharge tube said electrmmagnetbecornes deeenergised and permits ,the armature of the 4.0 relay to movebyattraction towards the other, and

energised, electro-rnagnet, such .movement being utilised to cause interruption of the current suptime the discharge, tube.

A device according to the present inventi'on 45' advantageously operates when either an opencircuit' or an earth fault occurs on the electric discharge-tube circuit. In an electric r iischarge-tube the appliedlpotential required, to set up the discharge is consid- 50. erably greaterTthan ,the potential. required to ,rna inta in the, discharge.- Where, transformer equipment with orwithouta choking coil is e m ployed to supply suchltubes it, is s9 designed that the current invtheflsecondary fcircuitremains approximately cohstantover ag'wide range. of loading, thus the voltage derived from the secondary ofthe transformer adjusts itself automatically to the impedance of the discharge-tube circuit to which the transformer is connected. Any leakage to earth on the secondary circuit tends to re- 5 duce the impedance of that circuit and so to cut down its terminal voltage. -If the leakage is considerable the voltage applied to the tube will become insufiicient to maintain the discharge,

so that the current through it falls practically 10' to zero.

' winding of the transformer is earthed a convenient arrangement is to employ two differential electromagnetic relays. One of these relays operates with an earth fault or open-circuit on one side of the earth point of the secondary circuit and'the second relay operates when similar conditions prevail on the other side of the earth lid:

point. The movement of the armatureof either relaylactuates a switch or fuse to interrupt the primary current of the transformer. In order that the invention may be clearly understood and carried into effect one embodiment 35,

of the "same, showing the use of a transformer with twodi'iierential relays, will now be described by aid of the accompanying diagram.

With reference to the accompanying drawing of a single-phase transformer, each of therelays U40 employed in this casehave two distinct electro magnets U and W supplied with currents derived respectively directly or through condensers from the secondary winding S and either an additional winding X with which is linked the primary flux, or froman'addition'al winding with which part of the primary flux only is linked, or from parallel or' series connection with the primary winding P itself. The armatures crand'cz are quite independent; Each is hinged at one end and-freejo to move? into contact with the poles of either one or other of their associated electromagnets.

Under ordinary operating conditions -'the:;armaturaCris held in contact with-the poles of electromagnet U1 and the armature C2 in contact with the poles of electromagnet U: the armatures remaining thus when the alternating current supply to. the terminals T is disconnected.

If an earth fault occurs on the left-hand side of the earth point E of the high voltage circuit the left-hand half of the'secondary winding becomes more heavily loaded due to the formation of the parallel circuit to earth. This causes a reduction of the terminal voltage of the secondary winding as a whole and if the change is sufiicient, ionisation in the discharge-tube N will cease and the current through it will fall almost to zero. In such circumstances the right-hand half of the secondary winding and with it the winding on the electromagnet U: will carry no current. The elect'romagnet W2 remains energised so that the armature C2 is pulled over into contact with the poles of W: and in so doing opens the .small mercury switch D by rocking it about the spindle H when the arm G2 strikes the projection F. At the same time the left-hand half of the secondary winding and with it the winding on the electromagnet U1 carries the earth leakage current and this will usually be sufficient to retain the armature C1 in contact with the poles of the electromagnet U1 but it is immaterial whether or not this armature is released at the same time.

If an earth fault occurs on the right-hand side of the earth point of the high voltage circuit the process is repeated with an interchange of the operation of the relays.

In the case of an open-circuit or interruption of the secondary circuit the currents through the windings of both electromagnets U1 and U2 are reduced to zero, whilst electromagnets W1 and W2 remain energised. The armatures C1 and C2 are pulled over into contact with the poles of W1 and W2 respectively, both operating to open the mercury switch D.

Since the mercury switch is connected by means of flexible leads L in series with the primary of the transformer, the supply is automatically interrupted under both earth fault and openrcuit conditions on the secondary.

The armatures C1 and C2 remain in the off positions untilreplaced in the ordinary working positions. 7 I

In practice it may be convenient to construct the apparatus so that one differential relay is placed vertically above the other, the two armatures being hinged about the same vertical spindle. The electromagnets Wrand We can then be combined into a single unit operating jointly on the two armatures.

In cases where the secondary winding of the transformer is earthedat one end a single differential relay with the accompanying. switch is suflicient.

.A single differential relay may also be employed when the earth potential point of the circuit through the discharge-tubes is accessible, such, for example, when several discharge tubes are connected in'series so that the winding U of the relay can be connected in series at that point. Alternatively the earth potential point may suitably be derived by forming such a subsidiary source A. C. or D. C. interrupted or otherwise,

the electromagnet W being energised in parallel with the supply.

In all cases the winding U of the differential 'relay must be connected at an earth potential alternatively to make the armatures cause a mechanical breakage of such fuses.

What I claim is:

1. An electrical protective device for gaseous electric discharge tubes comprising in combination two electromagnets which are normally energised by current from the discharge tube circuit one of said electromagnets becoming deenergised when an earth fault occurs in said circuit and the other electromagnet being de-energised when an open circuit occurs in said discharge tube circuit, an armature associated with each said electromagnet, and current interrupting means operatively associated with said armature the arrangement being such that de-energisation of either electromagnet releases its associated armature for movement to effect operform two differential relays one electromagnet in each pair being permanently connected in the discharge tube circuit, an armature associated with each pair of electromagnets, a separate circuit for permanently energising the other electromagnet in each pair, and current interrupting vmeans operatively associated with each said armature, the arrangement being such that said first mentioned electromagnets are alternatively tie-energised upon variation or interruption of the current through the discharge tube, the deenergisation of one said electromagnet taking place as a result of an open circuit and the other as a result of an earth fault, whilst the other and opposing permanently energised electromagnet operates to attract the armature of the de-energised electromagnet and eifect operation of the current interrupting means to cut off the current supply to the discharge tube circuit. I

3. An electrical protective device forgaseous electric discharge tubes comprising in combination, a static transformer supplying the discharge tubes four electromagnets arranged in pairs to form two diiferential relays one electromagnet in each pair being permanently connected in series with the secondary winding of the transformer, anarmature associated with each pair of electromagnets, an additional winding on the transformer core linked with the primary flux of the transformer for permanently energising the other electromagnet in each pair, and current interrupting means operatively associated with each said armature, the arrangement being such that said first mentioned electromagnets are alternatively de-energised upon variation ominterruption of the current through the discharge tube, the de-energisation of onesaid electromagnet taking place as a result of an open circuit and the other as a result of an earth fault, whilst the other and opposing permanently energised electromagnet operates to attract the armature of the de-energised electromagnet and eflect operation of the current interrupting means to cut off the current supply to the discharge tube circuit. '1

4. An electrical protective device for electric discharge tubes comprising in combination, a static transformer supplying the discharge tube, means for interrupting the current input to the primary winding of the transformer, two electromagnets in series with the secondary winding of the transformer, so as normally to be energised when current flows to the discharge tube, a

pivoted armature associated with each electromagnet to form a relay said armature being operatively associated with the current interrupting means in such manner that upon variation or interruption of the current through the discharge-tube the one or other of the electromagnets becomes deenergis'ed to permit movement. of its armature to effect operation of the current interrupting means to break the supply HAROLD EVERARD I MONTEAGLE BARLOW. 

